A few quick thoughts on the Western Conference finals in light of Serge Ibaka's calf injury, which is expected to sideline him for the rest of the playoffs:

• Given that injuries in the NBA are often viewed through the very practical lens of replacement, let's get one thing clear up front: Oklahoma City has no means to replace what's been lost. Nick Collison, Steven Adams and Kendrick Perkins are all useful in their own way, but none so much as Ibaka. He's a true rarity -- a game-changing defender who enables the Thunder to be as aggressive as is necessary on the perimeter all while helping to clear the paint on offense. Those Thunder big men next in line might help hedge against Ibaka's absence in some area or another, but none is as complete a player or as unnerving an interior defender.

Even the best scorers tend to get a bit jumpy when Ibaka lurks nearby, an influence that results in opponents altering the angle and timing on their shots or foregoing attempts entirely. That makes Ibaka plenty valuable in a general sense, though particularly so against the Spurs. If left to its own devices, San Antonio's offense will freewheel its way to open layups and three-pointers, whether for stars or role players. The team's balance is, in many ways, a construct; bit players don't suddenly improve upon arrival in San Antonio -- they're simply used in a way that helps foster opportunity without overstretch. The ball moves until it finds an open shot, and those who make plays along the way rarely have cause to step beyond their capabilities.

When these two teams meet, Ibaka helps challenge that dynamic. He's done a splendid job against Tim Duncan in recent games, with his length and strength in the post denying the Spurs a favorite option for fall-back offense. Beyond that, Ibaka's explosion as a help defender allows the Thunder to pursue the Spurs out to the three-point line without hesitation. It's his hovering that empowers Thabo Sefolosha to chase Danny Green off the three-point line, taking away a great look and replacing it with a fair one. The Ibaka-infused Thunder make the Spurs think. There is no autopilot, as careless passes will be picked off by eager defenders and thoughtless attempts will get swatted away by Ibaka himself. This is one of the only ways to disrupt the Spurs' mechanized efficiency, and it was the basis for San Antonio shooting just 42.3 percent from the field (and 33.3 percent from long range) while Ibaka was on the court this season.

• Coach Scott Brooks will rely on Collison and Adams more, but Ibaka's absence begs for the Thunder to run small as much as possible. The various two-man combinations among Collison, Adams and Perkins leave something to be desired; they won't be dominant defensively, lack seriously for offensive bite and aren't collectively strong enough on the glass to justify any prolonged run. This situation, instead, seems tailor-made for the smaller, punchier lineups that can help magnify what OKC's best players do well.

Brooks has relied on such configurations with increasing frequency over the past few seasons, as a change-of-pace variant and a situational counter. Here, though, I'm not sure there's much reasonable alternative to using the Thunder's smaller units as something of a default. Oklahoma City's offense isn't exactly built in such a way that Russell Westbrook and Kevin Durant can reasonably take on a bigger creative load. Those two rank first and second in playoff usage rate, respectively, as they dominate the Thunder's possessions by manufacturing shots, creating for others and getting to the free throw line. As such, it isn't likely that those two stars -- who average 58 points per game as it is -- can pick up the 12.2 points that Ibaka's absence leaves behind.

With that, going smaller is the most sensible way to address a potential scoring deficit. The Thunder bigs are good for utility points only -- Adams will get the odd roll to the rim, Collison can hit a few open jumpers and Perkins might net the occasional putback. Yet by keeping just one of those bigs on the floor with Westbrook, Durant, Reggie Jackson and either Caron Butler or Sefolosha, Oklahoma City at the very least would vacate the lane and give its offense some combustible material. Maxed-out spacing might be the Thunder's best bet.

• Let this injury and all others stand as a reminder of the role that luck -- cruel and uncompromising though it may be -- plays in winning or losing an NBA title. This is why it's silly to bag on individual players for a lack of playoff success. So many games and so many series rely on the ball bouncing this way or that, or some tiny, fragile tendon holding up under the thousandth jump of a player's season. It's why the idea of fitting any championship with an asterisk is patently ridiculous; every title is asterisked by its very nature, having been decided by countless tiny events that could broken any other way. It's why, no matter how much we dive into the nuances of the game and its finely tuned strategies, the most powerful force in play is often one beyond anyone's control.

As of Thursday the Thunder were clear contenders, triumphant in their series against a tough Clippers squad after surviving a grueling first-round matchup with the Grizzlies. On Friday they stand as very clear underdogs against the Spurs, not because the matchup dictates that to be so, but because Ibaka suffered a non-contact strain with a very high risk of re-injury. Oklahoma City's run doesn't completely unravel with that unfortunate break, but that chance happening significantly changes the character of the Western Conference finals and the NBA Finals.